1. Field of the Invention
The present invention relates to a compression moldable aromatic polyamide powder and a process for producing a compression molded article from the same. More particularly, the present invention relates to an aromatic polyamide powder in which particles of the aromatic polyamide are coalesced with each other into porous agglomerates and which is useful for compression molding and a process for producing a compression molded article having an enhanced impact resistance from the above-mentioned aromatic polyamide powder.
2. Description of the Related Art
It is known that an aromatic amide polymer consisting of recurring m-phenylene isophthalamide units exhibits excellent heat resistance and fire retardant property, and a satisfactory solubility in various solvents. Therefore, it is also known that the aromatic amide polymer is useful for producing fibers, films, and fibrids by a dry method or wet method. The poly(m-phenylene isophthalamide) fibers are known by the trademark TEIJINCONEX or NOMEX and are used in various fields.
The above-mentioned aromatic amide polymer is, however, disadvantageous in that the aromatic amide polymer cannot be shaped by means of a conventional metal-molding process. Therefore, the production of a shaped article having a large thickness from the aromatic amide polymer is difficult. The only known process for producing a shaped thick article from the aromatic amide polymer is disclosed in U.S. Pat. No. 3,925,323 for J. W. Turnbull or Japanese Unexamined Patent Publication (Kokai) No. 52-130,866 for E. I. Du Pont de Nemours and Company. In the known process, solid grains of the aromatic amide polymer are finely pulverized, the resultant power is preliminarily molded, and the resultant precursory molded article is sintered by heating it at a high temperature for a long period of time to form a shaped article.
In the above-mentioned process, a solution of the aromatic amide polymer is mixed with a precipitation reagent to convert the solution to a slurry, the slurry is homogenized by means of agitation and is filtered, the resultant solid particles of the aromatic amide polymer are collected, washed, and dried, the dried solid particles are pulverized into fine particles having an apparent bulk density of 0.2 g/cm.sup.2 or more and a surface are of 40 m.sup.2 /g, the fine particles are preliminarily molded under a pressure of 10,000 psi or more, and the resultant precursory molded article is sintered in an inert atmosphere at a temperature of 250.degree. C. to 350.degree. C. for several hours to provide a shaped and sintered aromatic amide polymer article.
The above-mentioned known process is disadvantageous not only in that the two steps of preliminary molding and sintering are necessary to shape the aromatic amide polymer powder, but also in that the sintering step must be carried out for a considerably long time to sufficiently sinter and bond the aromatic amide polymer particles to each other and to provide a sintered article having a satisfactory high mechanical strength.
Also, it has long been desired by industry to provide an aromatic amide polymer material useful for producing a shaped article having an enhanced impact resistance and a process for producing the enhanced impact resistant shaped article from the aromatic amide polymer material.